Normally a trap door is located in the vestibule of the rail car over steps. The trap door is hinged so that it can be moved between an upright vertical position and a downward horizontal position. This allows the conductor to permit a passenger to walk between the floor level of the car and a high station platform when the trap door is lowered. On the other hand, when a passenger goes between a low station platform and the floor level of the car, the trap door is raised to make accessible the steps below the trap door.
Elderly and handicapped persons, especially those confined to wheel chairs, have difficulty in boarding and leaving railway cars. This is particularly true when it is necessary to go up or down steps as when going from a lower station platform to the floor level of a vestibule of the car, or vice versa.